JP2020517837A - Iron ore pellets - Google Patents

Abstract

The present application describes pellets containing particulate iron ore and 0.05-1.0 wt% organic binder. The use of such pellets in an electric arc furnace for producing steel is also described. [Selection diagram] None

Description

The present invention relates to pellets containing iron ore for use in electric arc furnaces and methods of making steel from such pellets.

Briquette production from particulate iron and other metal ores is generally known in the art. Typically, such particles are combined using a binder such as cement or clay to form briquettes.

Such briquettes are used in blast furnaces or direct iron reduction (DRI). The briquettes are designed to be strong enough to successfully transport them and use them in the blast furnace. Briquettes must be able to maintain their integrity from the blast furnace to the melting furnace. Otherwise, the performance of the blast furnace or DRI plant may be adversely affected. A problem associated with the use of cement or clay is that the use of cement or clay increases the amount of silica in the iron and slag produced at the end of the process.

The high strength required for such briquettes has limited the use of more expensive binders such as starch and polyvinyl alcohol (PVA).

An electric arc furnace uses an electric arc to heat the charge material, for example between two graphite electrodes. An arc is formed between the charge material and the electrode. The charge material is heated by the electric current passing through the charge material and the radiant energy generated by the arc, which can reach 3000°C.

Electric arc furnaces are typically used to produce steel from scrap metal. Typically shreds (from white goods, automobiles or other lightweight steel) or heavy melts (large slabs of beams) are used. A problem with using scrap metal is that the input steel (and thus the steel produced) is often of poor quality. Steel often needs to have relatively expensive sponge iron or pig iron added to it. Scrap metal currently costs about $280 per ton, and sponge iron is often more expensive than this.

Applicants have recognized that using a cheaper source of iron allows steel to be produced at a lower cost using an arc furnace. One of the problems with using alternative sources such as iron ore is the need to reduce the iron ore to iron. This is typically not done in an arc furnace. However, Applicants have recognized that iron ore particulate waste can be used, provided that a reducing atmosphere can be used in the arc furnace.

The production of pellets for use in an arc furnace causes different problems than the conventional pellets used in a blast furnace. The pellets must be heavy enough to break the layer of slag at the top of the arc furnace. However, the pellets must also be sufficiently porous so that the iron ore in the pellets can react with the reducing atmosphere in the furnace to produce iron. The iron is then mixed with scrap metal to produce the required steel in the arc furnace. Also, the bond that holds the particles together must be sufficiently weak so that the particles melt and can be uniformly dispersed in the molten metal.

The use of particulate material increases the surface area of the iron oxide so that it can react more efficiently with the reducing atmosphere. Furthermore, the inventors have recognized that when using an organic binder, the binder burns out with the heat of the furnace, increasing the porosity of the pellets and reacting more easily with a reducing atmosphere. The cost of iron ore pellets is typically a 100% premium on the iron ore spot price. (The price of pellets is currently about $120 per ton). Therefore, this process can reduce the price of steel produced in an arc furnace.

In addition, the selection of cheaper reducing gases also helps reduce the cost of manufacturing steel using arc furnaces.

The present invention provides pellets comprising particulate iron ore and less than 1.5% by weight binder. The binder is typically an organic binder. As mentioned above, organic binders typically have the advantage of being burned out by the heat of the furnace, increasing the porosity of the material in the furnace. The particulate material is typically 4 mm or less in diameter, more typically less than 1 mm, or less than 500 microns, or less than 100 microns. This can be judged by whether it can pass through the sieve. Typically, at least 10% by weight of the particulate material can pass through a 100 μm sieve before being formed into pellets. More commonly, the material is screened using a sieve size of 30 μm or 20 μm. At least 50%, 80% or 100% of the material can pass through the screen.

It should be noted that the term "pellets" includes pellets, rods, objects commonly referred to as pencils slugs. The pellets typically have a maximum average diameter of 20 mm, more typically 16 mm or 15 mm, a minimum average diameter of 2 mm, especially 5 mm, or an average diameter of 10-12 mm. These objects share the common feature of being materials in compressed form and are distinguished primarily by their size and shape.

The binder can be a polymeric binder, for example selected from organic resins such as polyacrylamide resins, resole resins or novolac resins, and/or polysaccharides such as starch, hydroxyethylmethylcellulose, gum arabic, guar gum or xanthan gum. it can. Polysaccharides may be used as thickeners. Hydroxyethyl methylcellulose (MHEC) was found to have a particularly good shelf life. It may be mixed with an organic resin.

For example, the total amount of binder is 1.0 wt%, 0.8 wt%, 0.6 wt%, 0.5 wt%, at least 0.05 wt%, at least 0.1 wt%, or at least 0.2 wt%. It can be% by weight. The amount of polysaccharide to resin, when used in combination, can be 0.1 to 0.5 wt% polysaccharide, based on 0.5 to 0.1% resin.

Polyvinyl alcohol (PVA) may be used as a binder in an amount of 0 to 0.3% by weight, in particular 0.1 to 0.2% by weight, instead of or in addition to other binders. .. Polyvinyl alcohol is typically added in addition to other binders as needed to improve green strength and cure strength.

Examples of starches include, for example, wheat, corn and barley starch. More typically, the starch is potato starch because potato starch is relatively inexpensive.

Polyvinyl alcohol is typically formed commercially from polyvinyl acetate by replacing the acetate groups of the acetate with hydroxyl groups by reacting polyvinyl acetate with sodium hydroxide in a process called saponification. Partially saponified means that some of the acetate groups have been replaced by hydroxyl groups, thereby forming at least partially saponified polyvinyl alcohol residues.

Typically, PVA has a degree of saponification of at least 80%, typically at least 85%, at least 90%, at least 95%, at least 99%, or 100%. PVA is commercially available, for example, from Kuraray Europe GmbH in Germany. Typically it is utilized as an aqueous solution. PVA may be modified to include, for example, sodium hydroxide content.

Typically, PVA binders have an active polymer content of 12-13% and have a pH in the range of 4-6 when in solution.

Resols are base catalyzed phenol-formaldehyde resins with a formaldehyde to phenol ratio of greater than 1 (typically about 1.5). Novolac is a phenol-formaldehyde resin with a formaldehyde to phenol molar ratio of less than 1.

Typically, no additional binder, such as an inorganic binder, such as clay, is added to the particulate material.

In order to improve the wetting of iron by the additive, a trace amount of a surfactant such as SLS (sodium lauryl sulfate) may be added.

Typically iron ore is tailings or dust, for example from an electric furnace. The ore can be a magnetite _(Fe 3 _{O 4)} or hematite _(Fe 2 _{O 3).} The iron ore may contain naturally occurring pollutants.

The particulate iron ore may have a water content of less than 50%, more typically less than 30%, or less than 25%. Typically, the water content is at least 2% by weight, or at least 5% by weight or 10% by weight.

Twin-shaft batching mixtures are typically used to agglomerate the mixture. Overall, a press or extruder is typically used to form the pellets.

Waterproofing agents may be used to increase the weather resistance of the pellet material. The waterproofing agent may be combined with the particulate material or as a layer on the outer surface of the pellet, for example by spraying. Examples of waterproofing agents include styrene-acrylate copolymers and bituminous charcoal emulsions.

The pellets may further comprise up to 20% by weight carbonaceous material. The carbonaceous material can be, for example, coke, carbon black, peat or coal. The coal can be any grade of coal such as lignite, subbituminous coal, bituminous coal, steam coal or anthracite. The carbonaceous material is typically particulate and can have a particle size as defined above for iron particles.

The pellets may include less than 15 wt%, less than 10 wt%, or less than 5 wt% carbonaceous material.

The pellets are typically cold formed, for example without sintering, or heated to above 60°C, or above 40°C or 30°C before being placed in a furnace.

Also provided is a method of making steel comprising heating pellets according to the invention in a furnace, such as an arc furnace. Typically, the pellets are heated under a reducing atmosphere to convert iron ore into iron to be incorporated into steel. The reducing atmosphere may be, for example, hydrogen, shale gas or other natural gas. Hydrogen gas is often produced as a by-product from the processing of fossil fuels. Shale gas is natural gas that is trapped within the shale formation. Shale gas has become an increasingly important source of natural gas in the United States, with growing interest in other potential gas shales worldwide. Gas shale has become a relatively inexpensive source of natural gas. Alternative sources of natural gas include, for example, natural gas deposits in gas fields in the North Sea off the coast of the United Kingdom.

This method typically involves mixing the pellets with scrap metal. Typically, up to 50% by weight of the total of pellets and scrap metal are iron ore pellets. More typically, the amount of pellets used is less than 40%, less than 30%, less than 20%, or at least 5% of the mass of the pellets.

There is also provided a process for making pellets according to the invention, which comprises mixing the particulate iron ore with a binder up to 0.3% by weight. The binder and iron ore can be as defined above. As indicated above, twin shaft batch mixing is typically used to agglomerate the mixture. Typically, an extruder can be used to form pellets.

The amount of compression of the pellets can be varied, for example, by placing the mixture of particulate iron ore and binder under more or less vacuum, depending on the amount of compression required. Increasing the vacuum increases the compaction of the pellet. Alternatively, this may be controlled by the amount of pressure used to form the pellets.

The present invention is also a method for producing steel, in which the pellets according to the present invention produced by the method for producing the pellets according to the present invention are prepared as required, and the pellets are transported to an electric arc furnace to obtain the present invention. There is provided a method for producing steel, which comprises producing the steel by the method described in 1.

The pellets may be manufactured at a different location than where they are used. That is, the pellets are produced by pelletizing, for example, by combining with a binder where there is a deposit of fine iron ore, and then transported to an electric arc furnace at another geographical location. Transportation may be by ship, road or rail, for example.

Alternatively, the binder may be mixed with the particulate iron ore at substantially the same location as the arc furnace and then placed in the arc furnace.

The pellets can be placed in an arc furnace, for example, by a conveyor belt or by any other suitable means for transferring the pellets to the arc furnace.

The invention will now be described by way of example only.

Investigation of the reduction properties of cold-bonded iron ore pellets in a blast furnace Direct reduction and submerged arc furnace conditions Various samples were tested by the following method.
The pellets were placed in a small Inconel retort and surrounded by activated carbon granules. The vessel was closed and placed inside the muffle furnace. The furnace was cycled at various heats and times to simulate conditions in a full size plant.
The condition of the sample was evaluated when the sample was naturally cooled to room temperature.

1. Sample Type: 16×16 mm pellets with unmineralized ore, predominantly hematite powdered resole-type resin and binder including liquid polymer binder for green strength. Cold compression strength> 5kN.
Test cycle a. 600° C./30 minutes b. 600° C./2 hours c. 1000°C/1 hour Result:
a. The sample had microcracks that were easily visible under the microscope. The sample developed some magnetism indicating a reduction to magnetite.
b. The sample was very magnetic and expanded by 1-3% in size due to expansion cracking.
c. The sample cured and returned to full size.

2. Sample type: 16×16 mm pellets with binders including sorted ore, predominantly magnetite powdered resole type resin and liquid polymer binder for green strength. Cold compressive strength> 6 kN.
Test cycle a. 600° C./30 minutes b. 600° C./2 hours c. 1000° C./1 hour result a. No change was observed.
b. The pellet was essentially vesicular when viewed under a microscope.
c. Dimensional change-reduced by 5-10%, highly vesicular.

3. Sample type: mixed BF waste 16 x 16 mm pellets with binder including liquid polymer binder. Cold compressive strength >5 kN.
Test cycle a. 600° C./30 minutes b. 1100° C./1 hour result a. Color change and loss of intensity.
b. Highly vesicular, increased strength, evidence of sinter bonding.

4. Sample type: 32 x 32 mm pellets with mixed EAF dust organic liquid binder.
Test cycle a. 600° C./30 minutes b. 1000°C/1 hour result a-No change was observed.
b-Volume 25% reduction. A slight change in intensity.

Example:
Low grade hematite tailings with a size of 5.0-50 microns have a water content of 20%.
To the ore, add 0.5% anionic polyacrylamide powder in the size range-500 microns and mix in a high shear mixer.
As a production aid, a trace amount of surfactant such as SLS is added.
Extrude through a 15 mm opening using vacuum extrusion and cut into pellet sizes.
The water content before extrusion is 20% and after extrusion it is 16%.
The curing time is 24 hours at 25°C.
Test result: Compressive strength>250 kg/cm ²
RDI to ISO 4696-2 static = 36

6. High-grade magnetite concentrate with a density of 2.3 to 2.5 t/m ³ , a grade of 0 to 100 microns, and a water content of 13%±3. This is typical of many hematite ores when beneficiated to pellet grade.
To the ore is added a synthetic thickener such as high molecular weight hydroxyethylmethyl cellulose and 0.5% of a water soluble powdered novolac resin, then mixed in a high shear mixer.
Gums such as gum arabic, guar gum, and xantham gum can also be used, but have been found to have short shelf life in the field.
Extrude through a 15 mm opening using a vacuum extrusion and cut into pellet sizes. After curing for 24 hours at 25° C., the pellets have a strength above 250 kg/cm ² .
The thermal stability at 550 and 900°C is as follows.
550℃/1 hour Holds strength exceeding 50%.
900°C/1 hour Holds strength exceeding 60%.
PvOH can be added to the mixture at 0.1-0.2% to increase the green strength and cure strength to >400 kg/cm ² .

7. Electric arc furnace dust from baghouse filter:
An alternative binder is a 2% solution of high molecular weight MHEC. Add 5-10% and mix in high shear mixer.

Claims (14)

A pellet comprising particulate iron ore and an organic binder in an amount of 0.05 to 1.0 wt%, typically less than 0.3 wt%. The pellet of claim 1, wherein the organic binder is a polymeric organic binder. The pellet according to claim 1 or 2, wherein the organic binder is selected from polyacrylamide resin, resole resin, novolac resin, polyvinyl alcohol and polysaccharides. The pellet according to any one of claims 1 to 3, wherein the particulate iron ore has magnetism. The pellet according to any one of claims 1 to 4, which comprises a waterproofing agent. The pellet according to any one of claims 1 to 5, further comprising up to 20% by mass of carbonaceous material. The pellet according to any one of claims 1 to 6, wherein the particulate iron ore can pass through a 100 µm mesh before pelletization. A method for producing steel, comprising heating the pellet according to any one of claims 1 to 7 in an electric arc furnace. 9. The method of claim 8, wherein the pellets are heated under a reducing atmosphere. 10. The method according to claim 9, comprising heating under a reducing atmosphere containing hydrogen, shale gas or natural gas. A method according to any one of claims 8 to 10, comprising mixing with scrap metal. The method according to claim 11, wherein up to 50% by weight of the total of the pellets and scrap metal is composed of the iron ore pellets. The method for producing pellets according to any one of claims 1 to 7, which comprises mixing the particulate iron ore with a binder up to 0.3% by mass. The pellet according to any one of claims 1 to 7 produced by the method according to claim 13 is prepared as needed, and the pellet is transported to an electric arc furnace, and any of claims 8 to 13 is prepared. A method for producing steel, comprising producing the steel by the method according to claim 1.